Until recent times it was the practice to produce rotary blades, both fan and first stage compressor blades, with integral platforms. The relevant art is well known and will not be enlarged upon hereinafter. The mode of manufacture meant that blade and platform were of common, integral material and moreover, necessitated considerable working to achieve the platform shape.
Recent design trends have led to the obviation of integral blade/platform construction, at least in the design of ducted fans, and the inclusion of separate annulus fillers, which have their own features for removably locating them on the fan disc rim. Advantages afforded by such design are relative simplicity of manufacture, use of metals or other materials, e.g. composites, which are lighter than the blade metal, and easy replacement of damaged fillers. As regards the latter, damage to the platform of an integral blade/platform construction often meant replacing the whole.
Most damage incurred by the fan or first stage compressor structure immediately downstream of the fan is the result of the ingress of foreign objects, i.e. objects which range from birds to hailstones, and composite and lightweight metal parts tend to suffer more than heavier metal parts.